Genetic evidence of human adaptation to a cooked diet

Humans have been argued to be biologically adapted to a cooked diet, but this hypothesis has not been tested at the molecular level. Here, we combine controlled feeding experiments in mice with comparative primate genomics to show that consumption of a cooked diet influences gene expression and that affected genes bear signals of positive selection in the human lineage. Liver gene expression profiles in mice fed standardized diets of meat or tuber were affected by food type and cooking, but not by caloric intake or consumer energy balance. Genes affected by cooking were highly correlated with genes known to be differentially expressed in liver between humans and other primates, and more genes in this overlap set show signals of positive selection in humans than would be expected by chance. Sequence changes in the genes under selection appear before the split between modern humans and two archaic human groups, Neandertals and Denisovans, supporting the idea that human adaptation to a cooked diet had begun by at least 275,000 years ago

Social Influences on Inequity Aversion in Children

Adults and children are willing to sacrifice personal gain to avoid both disadvantageous and advantageous inequity. These two forms of inequity aversion follow different developmental trajectories, with disadvantageous inequity aversion emerging around 4 years and advantageous inequity aversion emerging around 8 years. Although inequity aversion is assumed to be specific to situations where resources are distributed among individuals, the role of social context has not been tested in children. Here, we investigated the influence of two aspects of social context on inequity aversion in 4- to 9-year-old children: (1) the role of the experimenter distributing rewards and (2) the presence of a peer with whom rewards could be shared. Experiment 1 showed that children rejected inequity at the same rate, regardless of whether the experimenter had control over reward allocations. This indicates that children’s decisions are based upon reward allocations between themselves and a peer and are not attempts to elicit more favorable distributions from the experimenter. Experiment 2 compared rejections of unequal reward allocations in children interacting with or without a peer partner. When faced with a disadvantageous distribution, children frequently rejected a smaller reward when a larger reward was visible, even if no partner would obtain the larger reward. This suggests that nonsocial factors partly explain disadvantageous inequity rejections. However, rejections of disadvantageous distributions were higher when the larger amount would go to a peer, indicating that social context enhances disadvantageous inequity aversion. By contrast, children rejected advantageous distributions almost exclusively in the social context. Therefore, advantageous inequity aversion appears to be genuinely social, highlighting its potential relevance for the development of fairness concerns. By comparing social and nonsocial factors, this study provides a detailed picture of the expression of inequity aversion in human ontogeny and raises questions about the function and evolution of inequity aversion in humans

Sex-specific association patterns in bonobos and chimpanzees reflect species differences in cooperation

In several group-living species, individuals' social preferences are thought to be influenced by cooperation. For some societies with fission–fusion dynamics, sex-specific association patterns reflect sex differences in cooperation in within- and between-group contexts. In our study, we investigated this hypothesis further by comparing sex-specific association patterns in two closely related species, chimpanzees and bonobos, which differ in the level of between-group competition and in the degree to which sex and kinship influence dyadic cooperation. Here, we used long-term party composition data collected on five chimpanzee and two bonobo communities and assessed, for each individual of 10 years and older, the sex of its top associate and of all conspecifics with whom it associated more frequently than expected by chance. We found clear species differences in association patterns. While in all chimpanzee communities males and females associated more with same-sex partners, in bonobos males and females tended to associate preferentially with females, but the female association preference for other females is lower than in chimpanzees. Our results also show that, for bonobos (but not for chimpanzees), association patterns were predominantly driven by mother–offspring relationships. These species differences in association patterns reflect the high levels of male–male cooperation in chimpanzees and of mother–son cooperation in bonobos. Finally, female chimpanzees showed intense association with a few other females, and male chimpanzees showed more uniform association across males. In bonobos, the most differentiated associations were from males towards females. Chimpanzee male association patterns mirror fundamental human male social traits and, as in humans, may have evolved as a response to strong between-group competition. The lack of such a pattern in a closely related species with a lower degree of between-group competition further supports this notion

Heterochrony in chimpanzee and bonobo spatial memory development

ObjectivesThe emergence of human‐unique cognitive abilities has been linked to our species’ extended juvenile period. Comparisons of cognitive development across species can provide new insights into the evolutionary mechanisms shaping cognition. This study examined the development of different components of spatial memory, cognitive mechanisms that support complex foraging, by comparing two species with similar life history that vary in wild ecology: bonobos (Pan paniscus) and chimpanzees (Pan troglodytes).Materials and methodsSpatial memory development was assessed using a cross‐sectional experimental design comparing apes ranging from infancy to adulthood. Study 1 tested 73 sanctuary‐living apes on a task examining recall of a single location after a 1‐week delay, compared to an earlier session. Study 2 tested their ability to recall multiple locations within a complex environment. Study 3 examined a subset of individuals from Study 2 on a motivational control task.ResultsIn Study 1, younger bonobos and chimpanzees of all ages exhibited improved performance in the test session compared to their initial learning experience. Older bonobos, in contrast, did not exhibit a memory boost in performance after the delay. In Study 2, older chimpanzees exhibited an improved ability to recall multiple locations, whereas bonobos did not exhibit any age‐related differences. In Study 3, both species were similarly motivated to search for food in the absence of memory demands.DiscussionThese results indicate that closely related species with similar life history characteristics can exhibit divergent patterns of cognitive development, and suggests a role of socioecological niche in shaping patterns of cognition in Pan.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/149316/1/ajpa23833_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/149316/2/ajpa23833.pd

Toshisada Nishida (1941–2011): Chimpanzee Rapport

Frans de Waal pays tribute to pioneering primatologist Toshisada Nishida, who transformed our understanding of chimpanzee behavior and culture and galvanized efforts to ensure their conservation

The Effect of Attractiveness on Food Sharing Preferences in Human Mating Markets

The current study explored how physical attractiveness affects food sharing by studying payment preferences for hypothetical romantic dinner dates (a hypothetical mating market). We analyzed payment preferences, self-rated attractiveness, and rated attractiveness for hypothetical dates in 416 participants. We hypothesized that (1) men would be more likely to prefer to pay than would women, (2) attractive individuals of both sexes would be less willing to pay, and (3) preferences to enter an exchange would be influenced by the attractiveness of prospective partners such that (3a) men would prefer to pay for attractive women, and (3b) women would prefer to be paid for by attractive men. All hypotheses were supported by our results. Individuals with higher self-rated attractiveness were more likely to prefer that their date would pay for the meal, and we found clear sex differences in how the attractiveness of potential dates affected payment preferences. Male participants preferred to pay for dates that had higher facial attractiveness, while female participants preferred that attractive men would pay. Individuals show condition dependent financial preferences consistent with the provisioning hypothesis in this mating market that are adaptive to evaluations of their own quality and that of prospective partners

A face for all seasons:searching for context-specific leadership traits and discovering a general preference for perceived health

Previous research indicates that followers tend to contingently match particular leader qualities to evolutionarily consistent situations requiring collective action (i.e., context-specific cognitive leadership prototypes) and information processing undergoes categorization which ranks certain qualities as first-order context-general and others as second-order context-specific. To further investigate this contingent categorization phenomenon we examined the “attractiveness halo”—a first-order facial cue which significantly biases leadership preferences. While controlling for facial attractiveness, we independently manipulated the underlying facial cues of health and intelligence and then primed participants with four distinct organizational dynamics requiring leadership (i.e., competition vs. cooperation between groups and exploratory change vs. stable exploitation). It was expected that the differing requirements of the four dynamics would contingently select for relatively healthier- or intelligent-looking leaders. We found perceived facial intelligence to be a second-order context-specific trait—for instance, in times requiring a leader to address between-group cooperation—whereas perceived health is significantly preferred across all contexts (i.e., a first-order trait). The results also indicate that facial health positively affects perceived masculinity while facial intelligence negatively affects perceived masculinity, which may partially explain leader choice in some of the environmental contexts. The limitations and a number of implications regarding leadership biases are discussed

Referential gestures are not ubiquitous in wild chimpanzees : alternative functions for exaggerated loud scratch gestures

Royal Zoological Society of Scotland for providing core funding for Budongo Conservation Field Station. This work was supported by the ERC grant awarded to KS (ERC_CoG 2016_724608).A fundamental aspect of human communication is our ability to refer to external objects and events through both words and gestures (such as pointing), yet the evolutionary origins of such signals remain obscure. Apes, living in their natural environments, rarely or never point, but it has been claimed that male chimpanzees, Pan troglodytes schweinfurthii, from the Ngogo community, Uganda, habitually use exaggerated loud scratches (ELSs) to refer to specific body locations where they wish to be groomed (Pika & Mitani, 2006, Current Biology, 16(6), 191–192). This study suggested continuity between referential abilities in humans and our closest living relatives, making it an important finding to replicate in other populations. Hence here, we compared whether ELSs are used in a referential manner across four wild communities of eastern chimpanzees (Ngogo, Kanyawara, Sonso and Waibira). Our data show that scratchers were significantly more likely to receive grooming in the scratched location at Ngogo compared to the other three sites. At the latter sites this response occurred at low rates and signallers did not seem to pursue this goal. This suggests that ELSs do not function referentially at these sites, and the published findings from Ngogo were not replicated. Further exploration into alternative functions of ELSs in the Kanyawara community revealed that, in this community, this signal functions to initiate grooming bouts and to reengage partners during grooming pauses. Individuals who produced the signal to initiate grooming were likely to offer grooming. In contrast, during grooming bouts, groomers produced ELSs to request reciprocation of grooming from their partner. Our study demonstrates that chimpanzees do not ubiquitously use the ELS in a referential manner, but that they can use this gesture in a highly flexible fashion, with signal function depending on the intricate details of the social contexts in which they are produced.Publisher PDFPeer reviewe

The functional significance of dental and mandibular reduction in Homo: A catarrhine perspective.

The reduction in dental size and mandibular robusticity is regarded as a major trend in human evolution, traditionally considered the result of the peculiar extra-oral food processing skills of Homo. The use of stone tools and fire would have allowed our ancestors to chew softer food in smaller bite size, thus relaxing the selective pressures to keep a large dentition and a robust lower jaw. This perspective assumes that differences in dental size and mandibular robusticity in hominins represent functional dissimilarities. This study uses a catarrhine comparative approach to test this fundamental assumption of the hypotheses on dental and mandibular reduction in Homo. A sample of extant catarrhines and fossil hominins was used to test for correlations between dental size, mandibular robusticity, and dietary proxies, the latter include diet quality, diet heterogeneity, feeding time, and microwear variables. The effects of phylogeny and body size were considered. Findings support the association between technological developments in Homo and reduction in incisor size and mandibular corpus robusticity, though not for premolar, molar size, and symphyseal robusticity. These results challenge the functional interpretation of postcanine reduction and symphyseal changes in the genus Homo